Synthesis of a Porphyrin-Fused π-Electron System

Abstract

Oligoporphyrins with a large fused π-electron system were successfully synthesized by the fusion of porphyrin chromophores with polycyclic aromatic hydrocarbons (PAHs). Oligoporphyrins fused with benzene units and zinc diporphyrins fused with PAHs were prepared and their electronic properties were examined. Electronic spectra showed strong absorption in the red to near-infrared (NIR) region. Not only the absorption maxima but also the number of absorption bands was affected by the fusion mode of the porphyrin chromophores. In the UV-vis spectra of the oligoporphyrins, three major absorption bands corresponding to Soret and Q bands were observed. A linearly fused trizinc triporphyrin with two benzene moieties showed strong Q-band absorption at 680nm, while split Q-band absorptions at 663 and 674nm were observed in the L-shaped triporphyrin. Preparation based on the retro-Diels-Alder reaction of the precursors with a bicyclo[2.2.2]octadiene skeleton did not give naphthacene- and pentacene-fused diporphyrins but instead gave naphthalene-, anthracene-, and chrysene-fused diporphyrins. In the chrysene-fused diporphyrin, the absorption maximum in the Q band was 624nm, which was similar to that of naphthalene-fused diporphyrin.